Epoxy resins are well known articles of commerce and are useful in many different applications. Advanced epoxy resins are prepared by reacting a low molecular weight epoxy resin with a polyhydric phenol in the presence of a catalyst. One particularly useful group of catalysts are the phosphonium catalysts as disclosed by Dante et al. in U.S. Pat. No. 3,477,990, Perry in U.S. Pat. No. 3,948,855, Tyler, Jr. et al. in U.S. Pat. No. 4,366,295 and Marshall in U.S. Pat. No. 4,634,757. In precatalyzed epoxy resin compositions, the ideal catalyst should be stable at elevated temperatures and not become deactivated during this prolonged storage. In the manufacture of advanced epoxy resins, the ideal catalyst should be sufficiently active such that the resulting product reaches its desired molecular weight or epoxide equivalent weight target value but not be so reactive at that point as to result in a product which is significantly beyond the target point as to molecular weight or epoxide equivalent weight. In other words, the catalyst should become essentially deactivated at the target point. While the catalysts of the aforementioned patents meet one or more of the above desirable characteristics of an ideal catalyst, none of them meets all of the characteristics of the ideal catalyst. It would be desirable to have a catalyst for the reaction between an epoxide compound and an acidic compound including aromatic hydroxyl containing compounds which has characteristics which meet or substantially meets the characteristics of the ideal catalyst.